Heat exchange tube and evaporator

ABSTRACT

An evaporator includes a plurality of flat heat exchange tubes extending in a vertical direction and arranged at intervals along a left-right direction with a width direction thereof coinciding with a front-rear direction. The heat exchange tube has a plurality of refrigerant channels arranged along the width direction. The evaporator satisfies a relation 0.558≦A≦1.235, where A is a value in pieces/mm obtained by dividing the number N of the refrigerant channels of the heat exchange tube by a width W of the heat exchange tube as measured in the front-rear direction. Also, the evaporator satisfies a relation 0.35≦Dh≦1.0, where Dh is an equivalent diameter in mm of the heat exchange tube. This evaporator can reduce the temperature difference between air discharged into a compartment when a compressor is turned ON and that when the compressor is turned OFF.

BACKGROUND OF THE INVENTION

The present invention relates to a heat exchange tube and an evaporator,and more particularly to a heat exchange tube preferably used in, forexample, an evaporator of a car air conditioner, which is arefrigeration cycle to be mounted on an automobile, as well as to anevaporator.

Herein and in the appended claims, the downstream side (a directionrepresented by arrow X in FIG. 1) of an air flow through air-passingclearances between adjacent heat exchange tubes will be referred to asthe “front,” and the opposite side as the “rear,” and the upper, lower,left-hand, and right-hand sides of FIG. 2 will be referred to as“upper,” “lower,” “left,” and “right,” respectively. Also, herein, theterm “aluminum” encompasses aluminum alloys in addition to purealuminum.

Conventionally, a so-called laminated evaporator has been widelyemployed as an evaporator for use in a car air conditioner. In thelaminated evaporator, a plurality of flat, hollow members, each of whichincludes a pair of depressed plates facing each other and brazed to eachother at their peripheral edge portions, are arranged in parallel, andcorrugate fins are each disposed between and brazed to the adjacentflat, hollow members.

In recent years, evaporators have been demanded to have furtherreduction in size and weight and to exhibit higher performance. Herein,the expression “higher performance” refers to the cooling performance ofa car air conditioner as observed when a compressor of the car airconditioner is ON. An evaporator which has been proposed to fulfillthose requirements (refer to, for example, Japanese Patent ApplicationLaid-Open (kokai) No. 2003-214794) includes a heat exchange core sectionin which heat exchange tube groups are arranged in two rows in afront-rear direction, each heat exchange tube group consisting of aplurality of heat exchange tubes arranged at intervals; a refrigerantinlet header section which is disposed on an upper-end side of the heatexchange tubes and to which the heat exchange tubes of a left half of afront heat exchange tube group are connected; a refrigerant outletheader section which is disposed on the upper-end side of the heatexchange tubes and rearward of the refrigerant inlet header section andto which the heat exchange tubes of a left half of a rear heat exchangetube group are connected; a first intermediate header section which isdisposed on a lower-end side of the heat exchange tubes and to which theheat exchange tubes connected to the refrigerant inlet header sectionare connected; a second intermediate header section which is disposedrightward of the first intermediate header section and to which theremaining heat exchange tubes of the front heat exchange group areconnected; a third intermediate header section which is disposed on theupper-end side of the heat exchange tubes and rightward of therefrigerant inlet header section and to which the heat exchange tubesconnected to the second intermediate header section are connected; afourth intermediate header section which is disposed on the upper-endside of the heat exchange tubes and rearward of the third intermediateheader section and to which the remaining heat exchange tubes of therear heat exchange group are connected; a fifth intermediate headersection which is disposed on the lower-end side of the heat exchangetubes and rearward of the second intermediate header section and towhich the heat exchange tubes connected to the fourth intermediateheader section are connected; and a sixth intermediate header sectionwhich is disposed on the lower-end side of the heat exchange tubes andleftward of the fifth intermediate header section and to which the heatexchange tubes connected to the refrigerant outlet header section areconnected. In the proposed evaporator, a refrigerant which has flowninto the refrigerant inlet header section flows through the heatexchange tubes and through the first to sixth intermediate headersections; flows into the refrigerant outlet header section; and thenflows out from the refrigerant outlet header section. The heat exchangetube used in the evaporator disclosed in the above publication is formedby bending an aluminum sheet into a flat form such that its widthdirection coincides with the air flow direction, and has an inner finarranged therein, thereby forming a plurality of channels arranged alongthe width direction.

Generally, in the case where a fixed-capacity-type compressor is used ina car air conditioner which uses an evaporator, the temperature of airat an outlet of the evaporator (discharge air temperature) is detectedby means of a thermistor, and on the basis of the detected discharge airtemperature, the compressor is controlled so as to be cyclically turnedON and OFF. Specifically, the compressor is controlled as follows: asshown by the broken line in FIG. 12, when the discharge air temperaturedrops to a preset low temperature t1 while the compressor is ON, thecompressor is turned OFF; subsequently, when the discharge airtemperature rises to a preset high temperature t2, the compressor isturned ON. In association with the ON-OFF operation of the compressor,air of a relatively low temperature and air of a relatively hightemperature are discharged into the compartment of an automobile incycles of a constant period.

In recent years, in order to further improve comfort in the compartmentof an automobile, reducing the temperature difference between airdischarged into the compartment when the compressor is turned ON andthat when the compressor is turned OFF has been contemplated. In thecase of the evaporator disclosed in the above publication, a simplemethod of reducing the temperature difference between air dischargedinto the compartment when the compressor is turned ON and that when thecompressor is turned OFF is to reduce the temperature difference betweenthe preset low temperature t1 and the preset high temperature t2 bymeans of lowering the preset high temperature t2. However, in this case,the compressor is frequently turned ON and OFF. This may have adverseeffect on the fuel economy of an automobile.

SUMMARY OF THE INVENTION

An object of the present invention is to solve the above problem and toprovide a heat exchange tube which, when used in an evaporator, enablesa reduction in the temperature difference between air discharged intothe compartment of an automobile when a compressor is turned ON and thatwhen the compressor is turned OFF, as well as an evaporator.

While conducting various studies, the inventors of the present inventionhave focused on heat exchange tubes and found that the temperaturedifference between air discharged into the compartment of an automobilewhen a compressor is turned ON and that when the compressor is turnedOFF can be reduced through improvement of retainability of liquid withinchannels of heat exchange tubes used in an evaporator. Specifically, wehave found the following: even after the compressor is turned OFF, whilea liquid-phase refrigerant remains in the channels of heat exchangetubes of the evaporator, heat exchange continues between the remainingliquid-phase refrigerant and air which passes through the evaporator, sothat an abrupt increase in discharge air temperature can be restrained.

The present invention has been accomplished based on the above findingsand comprises the following modes.

1) A heat exchange tube assuming a flat form and having a plurality ofchannels arranged along a width direction of the heat exchange tube,

the heat exchange tube satisfying a relation 0.558≦A≦1.235, where A is avalue in pieces/mm obtained by dividing the number N of the channels bya tube width W and is expressed by A=N/W.

In the heat exchange tube of par. 1), when A is less than 0.558, thecapillary effect fails to provide sufficient retainability of liquidwithin the channels of the heat exchange tube. Accordingly, in arefrigeration cycle having an evaporator in which the heat exchangetubes are used with their longitudinal direction coinciding with thevertical direction, when a compressor is turned OFF, a refrigerant flowsout from the channels of the heat exchange tubes in a short period oftime. This causes an abrupt increase in discharge air temperature of theevaporator. When A is greater than 1.235, the capillary effect providesimproved retainability of liquid within the channels of the heatexchange tube. Accordingly, in a refrigeration cycle having anevaporator in which the heat exchange tubes are used with theirlongitudinal direction coinciding with the vertical direction, when acompressor is turned OFF, there can be prevented outflow of refrigerantfrom the channels of the heat exchange tubes in a short period of time.However, cooling performance while the compressor is ON deteriorates.

2) A heat exchange tube assuming a flat form and having a plurality ofchannels arranged along a width direction of the heat exchange tube,

the heat exchange tube satisfying a relation 0.35≦Dh≦1.0, where Dh is anequivalent diameter in mm.

As well known, the equivalent diameter appearing in the heat exchangetube of par. 2) has the following meaning. The heat exchange tube havinga plurality of noncircular channels is considered as a circular tubehaving a single circular channel. The equivalent diameter means thediameter of the circular channel and is defined by

Dh=4Ac/Pi

where Ac is the total cross-sectional area of the plurality of channels,and Pi is the total cross-sectional, perimetric length of the pluralityof channels.

In the heat exchange tube of par. 2), when Dh is less than 0.35, thecapillary effect provides improved retainability of liquid within thechannels of the heat exchange tubes. Accordingly, in a refrigerationcycle having an evaporator in which the heat exchange tubes are usedwith their longitudinal direction coinciding with the verticaldirection, when a compressor is turned OFF, there can be preventedoutflow of refrigerant from the channels of the heat exchange tubes in ashort period of time. However, cooling performance while the compressoris ON deteriorates. When Dh is greater than 1.0, the capillary effectfails to provide sufficient retainability of liquid within the channelsof the heat exchange tubes. Accordingly, in a refrigeration cycle havingan evaporator in which the heat exchange tubes are used with theirlongitudinal direction coinciding with the vertical direction, when acompressor is turned OFF, a refrigerant flows out from the channels ofthe heat exchange tubes in a short period of time. This causes an abruptincrease in discharge air temperature of the evaporator as well as adrop in cooling performance while the compressor is ON.

3) A heat exchange tube according to par. 1) or 2), wherein each of allthe channels excluding two channels located at widthwise opposite endshas an elongated protrusion formed on an inner peripheral surface of thechannel and extending in a longitudinal direction of the channel.

4) A heat exchange tube according to par. 1) or 2), wherein each of allthe channels excluding two channels located at widthwise opposite endshas a rectangular cross section, and a corner portion of the rectangularcross section has a radius R of 0.1 mm or less.

5) A heat exchange tube according to par. 1) or 2), comprising two flatwalls in parallel with each other; first and second side walls extendingbetween and over corresponding side ends of the two flat walls; andpartition walls provided between the first and second side walls andextending between the two flat walls and in a longitudinal direction ofthe two flat walls for separating the adjacent channels from each other;

-   -   wherein the heat exchange tube is formed from a single metal        sheet including two flat-wall-forming portions; a connection        portion connecting the two flat-wall-forming portions and        adapted to form the first side wall; two side-wall-forming        elongated projections provided integrally with and in such a        manner as to project from corresponding side ends of the        flat-wall-forming portions on sides opposite the connection        portion, and adapted to form the second side wall; and a        plurality of partition-wall-forming elongated projections        provided integrally with the flat-wall-forming portions in such        a manner as to project in the same direction as the        side-wall-forming elongated projections;

the heat exchange tube is formed by folding the metal sheet at theconnection portion into a hairpin form such that the side-wall-formingelongated projections butt against each other, and brazing the buttingside-wall-forming elongated projections together; and

the partition-wall-forming elongated projections of at least eitherflat-wall-forming portion form the partition walls.

6) An evaporator comprising a plurality of heat exchange tubes eachassuming a flat form, the heat exchange tubes being arranged atintervals along a left-right direction with a width direction of theheat exchange tubes coinciding with a front-rear direction, the heatexchange tubes extending in a vertical direction, and each of the heatexchange tubes having a plurality of refrigerant channels arranged alongthe width direction,

-   -   the evaporator satisfying a relation 0.558≦A≦1.235, where A is a        value in pieces/mm obtained by dividing the number N of the        refrigerant channels of the heat exchange tube by a width W of        the heat exchange tube as measured in the front-rear direction        and is expressed by A=N/W.

7) An evaporator comprising a plurality of heat exchange tubes eachassuming a flat form, the heat exchange tubes being arranged atintervals along a left-right direction with a width direction of theheat exchange tubes coinciding with a front-rear direction, the heatexchange tubes extending in a vertical direction, and each of the heatexchange tubes having a plurality of refrigerant channels arranged alongthe width direction,

-   -   the evaporator satisfying a relation 0.35≦Dh≦1.0, where Dh is an        equivalent diameter in mm of the heat exchange tube.

8) An evaporator according to par. 6) or 7), wherein each of all therefrigerant channels of the heat exchange tube excluding two refrigerantchannels located at widthwise opposite ends has an elongated protrusionformed on an inner peripheral surface of the refrigerant channel andextending in a longitudinal direction of the refrigerant channel.

9) An evaporator according to par. 6) or 7), wherein each of all therefrigerant channels of the heat exchange tube excluding two refrigerantchannels located at widthwise opposite ends has a rectangular crosssection, and a corner portion of the rectangular cross section has aradius R of 0.1 mm or less.

10) An evaporator according to par. 6) or 7), wherein each of the heatexchange tubes comprises two flat walls in parallel with each other;first and second side walls extending between and over correspondingside ends of the two flat walls; and partition walls provided betweenthe first and second side walls and extending between the two flat wallsand in a longitudinal direction of the two flat walls for separating theadjacent refrigerant channels from each other;

the heat exchange tube is formed from a single metal sheet including twoflat-wall-forming portions; a connection portion connecting the twoflat-wall-forming portions and adapted to form the first side wall; twoside-wall-forming elongated projections provided integrally with and insuch a manner as to project from corresponding side ends of theflat-wall-forming portions on sides opposite the connection portion, andadapted to form the second side wall; and a plurality ofpartition-wall-forming elongated projections provided integrally withthe flat-wall-forming portions in such a manner as to project in thesame direction as the side-wall-forming elongated projections;

the heat exchange tube is formed by folding the metal sheet at theconnection portion into a hairpin form such that the side-wall-formingelongated projections butt against each other, and brazing the buttingside-wall-forming elongated projections together; and

the partition-wall-forming elongated projections of at least eitherflat-wall-forming portion form the partition walls.

11) An evaporator according to par. 6) or 7), further comprising:

a refrigerant inlet/outlet header tank having a refrigerant inlet headersection and a refrigerant outlet header section arranged injuxtaposition in the front-rear direction;

a refrigerant turn header tank disposed below and apart from therefrigerant inlet/outlet header tank and having a first intermediateheader section opposed to the refrigerant inlet header section, and asecond intermediate header section opposed to the refrigerant outletheader section and communicating with the first intermediate headersection; and

a heat exchange core section formed between the refrigerant inlet/outletheader tank and the refrigerant turn header tank;

wherein the heat exchange core section comprises a heat exchange tubegroup consisting of a plurality of heat exchange tubes arranged atintervals in a longitudinal direction of the refrigerant inlet/outletand turn header tanks and connected, at opposite end portions, to therefrigerant inlet/outlet and turn header tanks, and fins each disposedbetween adjacent heat exchange tubes;

two or more heat exchange tube groups are arranged between therefrigerant inlet/outlet and turn header tanks and in juxtaposition inan air flow direction; and

the heat exchange tubes of at least one heat exchange tube group areconnected between the refrigerant inlet header section and the firstintermediate header section, and the heat exchange tubes of at least oneheat exchange tube group are connected between the refrigerant outletheader section and the second intermediate header section.

According to the heat exchange tube of par. 1) or 2), the capillaryeffect provides improved retainability of liquid within the channels ofthe heat exchange tube. Accordingly, in a refrigeration cycle having anevaporator in which the heat exchange tubes are used with theirlongitudinal direction coinciding with the vertical direction, even whena compressor is turned OFF, a liquid-phase refrigerant is retainedwithin the channels of the heat exchange tubes for a relatively longperiod of time by virtue of the capillary effect, thereby preventingoutflow of the liquid-phase refrigerant from the channels of the heatexchange tubes in a short period of time. Additionally, even after thecompressor is turned OFF, while the liquid-phase refrigerant remainswithin the channels of the heat exchange tubes of the evaporator, heatexchange continues between the remaining liquid-phase refrigerant andair passing through the evaporator, so that an abrupt increase indischarge air temperature can be restrained. As a result, in the casewhere the compressor is controlled on the basis of discharge airtemperature of the evaporator, the preset high temperature can be setlower than in the case of the evaporator disclosed in the abovepublication. Therefore, the temperature difference between airdischarged into a compartment of an automobile when the compressor isturned ON and that when the compressor is turned OFF can be reduced,thereby improving comfort in the compartment. Furthermore, an abruptincrease in discharge air temperature after the compressor is turned OFFcan be restrained. Thus, in the case where the compressor is controlledon the basis of discharge air temperature of the evaporator, even whenthe preset high temperature is set lower than in the case of theevaporator disclosed in the above publication, the cycle of turning ONand OFF the compressor can have the same period as in the case where thecompressor is used in combination with the evaporator disclosed in theabove publication. Therefore, as opposed to the case where theevaporator disclosed in the above publication is used, the compressordoes not frequently go ON and OFF, so that the fuel economy of anautomobile is not adversely effected.

According to the heat exchange tube of par. 3) or 4), the capillaryeffect provides further improved retainability of liquid within thechannels of the heat exchange tube.

According to the evaporator of par. 6) or 7), the capillary effectprovides improved retainability of liquid within the channels of theheat exchange tubes. Accordingly, in a refrigeration cycle having thisevaporator, even when a compressor is turned OFF, a liquid-phaserefrigerant is retained within the channels of the heat exchange tubesfor a relatively long period of time by virtue of the capillary effect,thereby preventing outflow of the liquid-phase refrigerant from thechannels of the heat exchange tubes in a short period of time.Additionally, even after the compressor is turned OFF, while theliquid-phase refrigerant remains within the channels of the heatexchange tubes of the evaporator, heat exchange continues between theremaining liquid-phase refrigerant and air passing through theevaporator, so that an abrupt increase in discharge air temperature canbe restrained. As a result, in the case where the compressor iscontrolled on the basis of discharge air temperature of the evaporator,the preset high temperature can be set lower than in the case of theevaporator disclosed in the above publication. Therefore, thetemperature difference between air discharged into a compartment of anautomobile when the compressor is turned ON and that when the compressoris turned OFF can be reduced, thereby improving comfort in thecompartment. Furthermore, an abrupt increase in discharge airtemperature after the compressor is turned OFF can be restrained. Thus,in the case where the compressor is controlled on the basis of dischargeair temperature of the evaporator, even when the preset high temperatureis set lower than in the case of the evaporator disclosed in the abovepublication, the cycle of turning ON and OFF the compressor can have thesame period as in the case where the compressor is used in combinationwith the evaporator disclosed in the above publication. Therefore, asopposed to the case where the evaporator disclosed in the abovepublication is used, the compressor does not frequently go ON and OFF,so that the fuel economy of an automobile is not adversely effected.

According to the evaporator of par. 8) or 9), the capillary effectprovides further improved retainability of liquid within the channels ofthe heat exchange tubes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially cut-away perspective view showing the overallconfiguration of an evaporator according to the present invention;

FIG. 2 is a fragmentary view in vertical section showing the evaporatorof FIG. 1 with its intermediate portion omitted as it is seen from therear;

FIG. 3 is an enlarged fragmentary view in section taken along line A-Aof FIG. 2;

FIG. 4 is a cross-sectional view showing a heat exchange tube of theevaporator of FIG. 1;

FIG. 5 is an exploded perspective view of a refrigerant inlet/outletheader tank of the evaporator of FIG. 1;

FIG. 6 is a sectional view taken along line B-B of FIG. 2;

FIG. 7 is an enlarged sectional view taken along line C-C of FIG. 6;

FIG. 8 is a sectional view taken along line D-D of FIG. 7;

FIG. 9 is a partially cut-away perspective view showing a right-handclosing member and a joint plate for the refrigerant inlet/outlet headertank of the evaporator of FIG. 1;

FIG. 10 is an exploded perspective view of a refrigerant turn headertank of the evaporator of FIG. 1;

FIG. 11 is a sectional view taken along line E-E of FIG. 2;

FIG. 12 is a graph showing variation of discharge air temperature when afixed-capacity-type compressor is turned ON and OFF in a car airconditioner which uses an evaporator;

FIGS. 13 a to 13 e are cross-sectional views showing heat exchange tubesused in evaporators of Examples 2 to 5 and Comparative Example;

FIG. 14 is a graph showing the relationship of equivalent diameter withcooling performance and the amount of remaining liquid-phaserefrigerant;

FIG. 15 is a graph showing the relationship of the number of refrigerantchannels with cooling performance and the amount of remainingliquid-phase refrigerant;

FIG. 16 is a cross-sectional view showing a modified heat exchange tube;

FIG. 17 is a fragmentary enlarged view of FIG. 16;

FIGS. 18 a to 18 c are views showing a method of manufacturing the heatexchange tube of FIGS. 16 and 17; and

FIG. 19 is a cross-sectional view showing another modified heat exchangetube.

DESCRIPTION OF THE PREFERRED EMBODIMENT

An embodiment of the present invention will next be described in detailwith reference to the drawings. The embodiment is implemented byapplying a heat exchange tube according to the present invention to anevaporator of a car air conditioner using a chlorofluorocarbon-basedrefrigerant.

FIGS. 1 and 2 show the overall configuration of an evaporator, and FIGS.3 to 11 show the configuration of essential portions of the evaporator.

As shown in FIGS. 1 to 3, an evaporator 20 is configured such that aheat exchange core section 21 is provided between a refrigerantinlet/outlet header tank 22 and a refrigerant turn header tank 23. Therefrigerant inlet/outlet header tank 22 and the refrigerant turn headertank 23 are made of aluminum and are vertically spaced apart from eachother.

The refrigerant inlet/outlet header tank 22 includes a refrigerant inletheader section 24 located on a side toward the front (downstream sidewith respect to the air flow direction), a refrigerant outlet headersection 25 located on a side toward the rear (upstream side with respectto the air flow direction), and a connection section 26 which integrallyconnects the header sections 24 and 25. A refrigerant inlet pipe 27 madeof aluminum is connected to the refrigerant inlet header section 24 ofthe refrigerant inlet/outlet header tank 22. A refrigerant outlet pipe28 made of aluminum is connected to the refrigerant outlet headersection 25.

The refrigerant turn header tank 23 includes a first intermediate headersection 30 located on the side toward the front, a second intermediateheader section 31 located on the side toward the rear, and a connectionsection 32 which integrally connects the header sections 30 and 31. Theheader sections 30 and 31 and the connection section 32 form a draingutter 33.

The heat exchange core section 21 is configured as follows: heatexchange tube groups 35 are arranged in a plurality of; herein, two,rows in the front-rear direction, each heat exchange tube group 35consisting of a plurality of heat exchange tubes 34 arranged in parallelat intervals in the left-right direction; corrugated fins 36 aredisposed within corresponding air-passing clearances between theadjacent heat exchange tubes 34 of the heat exchange tube groups 35 andexternally of the left-end and right-end heat exchange tubes 34 of theheat exchange tube groups 35 and are brazed to the corresponding heatexchange tubes 34; and side plates 37 made of aluminum are disposedexternally of the left-end and right-end corrugated fins 36 and arebrazed to the corresponding corrugated fins 36. Upper and lower ends ofthe heat exchange tubes 34 of the front heat exchange tube group 35 areconnected to the refrigerant inlet header section 24 and the firstintermediate header section 30, respectively, whereby the heat exchangetubes 34 form a forward refrigerant flow section. Upper and lower endsof the heat exchange tubes 34 of the rear heat exchange tube group 35are connected to the refrigerant outlet header section 25 and the secondintermediate header section 31, respectively, whereby the heat exchangetubes 34 form a return refrigerant flow section. The first intermediateheader section 30, the second intermediate header section 31, and theheat exchange tubes 34 of the front and rear heat exchange tube groups35 form a refrigerant circulation path for establishing communicationbetween the refrigerant inlet header section 24 and the refrigerantoutlet header section 25.

The heat exchange tube 34 is formed from a bare aluminum extrudate. Asshown in FIG. 4, the heat exchange tube 34 assumes a flat form with itswidth direction coinciding with the front-rear direction and has aplurality of refrigerant channels 34 a arranged along the widthdirection. The heat exchange tube 34 includes flat left and right walls341 and 342 facing each other; front and rear side walls 343 and 344extending between and over corresponding side ends of the left and rightflat walls 341 and 342; and partition walls 345 provided between thefront and rear side walls 343 and 344 and extending between the left andright walls 341 and 342 and in a longitudinal direction of the left andright walls 341 and 342 for separating the adjacent refrigerant channels34 a from each other. Each of all the refrigerant channels 34 a of theheat exchange tube 34 excluding two refrigerant channels 34 a located atwidthwise opposite ends has two or more; in the present embodiment,four, elongated protrusions 346 formed on an inner peripheral surface ofthe refrigerant channel 34 a and extending in a longitudinal directionof the refrigerant channel 34 a. That is, in each of all the refrigerantchannels 34 a of the heat exchange tube 34 excluding two refrigerantchannels 34 a located at widthwise opposite ends, the two elongatedprotrusions 346 are formed on the inner surface of each of the left andright walls 341 and 342 in such a manner as to be spaced apart from eachother in the front-rear direction. Also, each of all the refrigerantchannels 34 a excluding two refrigerant channels 34 a located atwidthwise opposite ends has a rectangular cross section, and cornerportions 34 b of the rectangular cross section each have a radius R of0.1 mm or less. Each of the front and rear side walls 343 and 344 of theheat exchange tube 34 has such an arcuate cross section that a centralportion projects outward. The front heat exchange tubes 34 and the rearheat exchange tubes 34 are arranged so as to be identical in position inthe left-right direction. The front heat exchange tubes 34 communicatewith the refrigerant inlet header section 24 and the first intermediateheader section 30. The rear heat exchange tubes 34 communicate with therefrigerant outlet header section 25 and the second intermediate headersection 31.

The heat exchange tube 34 satisfies a relation 0.558 ≦A≦1.235, where Ais a value in pieces/mm obtained by dividing the number N of therefrigerant channels 34 a by a width W of the heat exchange tube 34 asmeasured in the front-rear direction and is expressed by A=N/W. Also,the heat exchange tube 34 satisfies a relation 0.35≦Dh≦1.0, where Dh isan equivalent diameter in mm of the heat exchange tube 34. The heatexchange tube 34 satisfies one of or both of the above two requirements.

The corrugated fin 36 is made in a wavy form from an aluminum brazingsheet having a brazing material layer on each of opposite sides thereof.The corrugated fin 36 includes wave crest portions, wave troughportions, and flat horizontal connection portions each connectingtogether the wave crest portion and the wave trough portion. A pluralityof louvers are formed at the connection portions in juxtaposition in thefront-rear direction. The front and rear heat exchange tubes 34 whichconstitute the front and rear heat exchange tube groups 35 share thecorresponding corrugated fins 36. The width of the corrugated fin 36 asmeasured in the front-rear direction is substantially equal to the spanbetween the front end of the front heat exchange tube 34 and the rearend of the rear heat exchange tube 34. The wave crest portions and wavetrough portions of the corrugated fin 36 are brazed to the front andrear heat exchange tubes. Notably, the front end of the corrugated fin36 slightly projects frontward beyond the front end of the front heatexchange tube 34.

As shown in FIGS. 3, 5, and 6, the refrigerant inlet/outlet header tank22 is formed from an aluminum brazing sheet having a brazing materiallayer on each of opposite sides thereof, and includes a first member 38assuming a plate-like form and to which all the heat exchange tubes 34are connected; a second member 39 formed from a bare aluminum extrudateand covering the upper side of the first member 38; and closing members41 and 42 formed from an aluminum brazing sheet having a brazingmaterial layer on each of opposite sides thereof, and joined to theopposite ends of the first and second members 38 and 39. A joint plate43 made of aluminum and elongated in the front-rear direction is brazedto the outer surface of the right-hand closing member 42 while facingthe ends of the refrigerant inlet header section 24 and the refrigerantoutlet header section 25. The refrigerant inlet pipe 27 and therefrigerant outlet pipe 28 are connected to the joint plate 43.

The first member 38 includes a first header formation portion 44, whichassumes a downward bulging form and forms a lower portion of therefrigerant inlet header section 24; a second header formation portion45, which assumes a downward bulging form and forms a lower portion ofthe refrigerant outlet header section 25; and a connection wall 46,which connects a rear end portion of the first header formation portion44 and a front end portion of the second header formation portion 45 andforms a lower portion of the connection section 26. A plurality of tubeinsertion holes 47 elongated in the front-rear direction are formed inthe header formation portions 44 and 45 at intervals in the left-rightdirection. The tube insertion holes 47 of the header formation portion44 and those of the header formation portion 45 are identical inposition in the left-right direction. Upper end portions of the heatexchange tubes 34 of the front and rear heat exchange tube groups 35 ofthe heat exchange core section 21 are inserted into the respective tubeinsertion holes 47 of the first and second header formation portions 44and 45 and are brazed to the first member 38 by utilization of thebrazing material layers of the first member 38. Thus, the upper endportions of the heat exchange tubes 34 of the front heat exchange tubegroup 35 are connected to the refrigerant inlet header section 24 in acommunicating condition, whereas the upper end portions of the heatexchange tubes 34 of the rear heat exchange tube group 35 are connectedto the refrigerant outlet header section 25 in a communicatingcondition. A plurality of drain through-holes 48 elongated in theleft-right direction are formed in the connection wall 46 at intervalsin the left-right direction. Also, a plurality of fixation though-holes49 are formed in the connection wall 46 at intervals in the left-rightdirection while being shifted from the drain through-holes 48.

The second member 39 includes a first header formation portion 51, whichassumes an upward bulging form and forms an upper portion of therefrigerant inlet header section 24; a second header formation portion52, which assumes an upward bulging form and forms an upper portion ofthe refrigerant outlet header section 25; and a connection wall 53,which connects a rear end portion of the first header formation portion51 and a front end portion of the second header formation portion 52 andis brazed to the connection wall 46 of the first member 38 to form anupper portion of the connection section 26. The first header formationportion 51 has a horizontal intra-inlet-header-section flow-dividingcontrol wall 51 b, which integrally connects lower end portions of frontand rear walls 51 a of the first header formation portion 51 andvertically divides the interior of the refrigerant inlet header section24 into two spaces 24A and 24B. The second header formation portion 52has a horizontal intra-outlet-header-section flow-dividing control wall52 b, which is at the same level as that of theintra-inlet-header-section flow-dividing control wall 51 b, integrallyconnects lower end portions of front and rear walls 52 a of the secondheader formation portion 52, and vertically divides the interior of therefrigerant outlet header section 25 into two spaces 25A and 25B.

A cutout 50 is formed at the left end of the intra-inlet-header-sectionflow-dividing control wall 51 b of the second member 39. Theintra-inlet-header-section flow-dividing control wall 51 b hasflow-division-adjusting holes 60, which are formed in a through-holeform at a portion biased toward the cutout 50 and at a portion biasedtoward the right end. A plurality of oblong refrigerant passage holes54A and 54B in a through-hole form and elongated in the left-rightdirection are formed in a rear region, excluding left and right endportions thereof, of the intra-outlet-header-section flow-dividingcontrol wall 52 b of the second member 39 at intervals in the left-rightdirection. The central oblong refrigerant passage hole 54A is shorterthan the other oblong refrigerant passage holes 54B and is locatedbetween the adjacent heat exchange tubes 34.

A plurality of drain through-holes 55 elongated in the left-rightdirection are formed in the connection wall 53 of the second member 39in alignment with the corresponding drain through-holes 48 of the firstmember 38. Also, a plurality of projections 56 are formed on theconnection wall 53 in alignment with the corresponding fixationthrough-holes 49 of the first member 38 and are fitted into thecorresponding fixation through-holes 49. The first member 38 and thesecond member 39 are assembled together as follows. The first and secondmembers 38 and 39 are tentatively assembled together such that theprojections 56 are tightly inserted into the corresponding fixationthrough-holes 49. In this tentatively assembled condition, byutilization of the brazing material layers of the first member 38, thefirst and second members 38 and 39 are assembled together such thatfront end portions of the first header formation portions 44 and 51,rear end portions of the second header formation portions 45 and 52, andthe connection walls 46 and 53 are respectively brazed together.

The first header formation portion 44 of the first member 38 and thefirst header formation portion 51 of the second member 39 form a hollowinlet header section body 240 whose opposite ends are open. The secondheader formation portion 45 of the first member 38 and the second headerformation portion 52 of the second member 39 form a hollow outlet headersection body 250 whose opposite ends are open.

The left-hand closing member 41 is formed such that a front cap 41 a forclosing the left end opening of the inlet header section body 240 and arear cap 41 b for closing the left end opening of the outlet headersection body 250 are integrated with each other via a connection portion41 c. The front cap 41 a of the left-hand closing member 41 has anintegrally formed rightward projecting portion 57 to be fitted into theinlet header section body 240. Similarly, the rear cap 41 b has anintegrally formed upper rightward-projecting portion 58 to be fittedinto a space of the outlet header section body 250 located above theintra-outlet-header-section flow-dividing control wall 52 b, and anintegrally formed lower rightward-projecting portion 59 to be fittedinto a space of the outlet header section body 250 located below theintra-outlet-header-section flow-dividing control wall 52 b. The upperrightward-projecting portion 58 and the lower rightward-projectingportion 59 are vertically spaced apart from each other. Engagementfingers 61 projecting rightward are formed integrally with the left-handclosing member 41 at a connection portion between a front side edge anda top edge of the left-hand closing member 41, at a connection portionbetween the front side edge and a bottom edge, at a connection portionbetween a rear side edge and the top edge, and at a connection portionbetween the rear side edge and the bottom edge, respectively. Theengagement fingers 61 are engaged with the first and second members 38and 39. The left-hand closing member 41 is brazed to the first andsecond members 38 and 39 by utilization of its own brazing materiallayers. The front cap 41 a of the left-hand closing member 41 closes theleft end opening of the cutout 50 of the intra-inlet-header-sectionflow-dividing control wall 51 b, thereby forming a communication hole 70for establishing communication between the upper and lower spaces 24Aand 24B of the inlet header section 24 at a left end portion of theinlet header section 24. In the present embodiment, the communicationhole 70 is formed by means of closing the left end opening of the cutout50 by the front cap 41 a. However, instead of formation of a cutout, athrough-hole may be formed at a left end portion of theintra-inlet-header-section flow-dividing control wall 51 b so as toserve as a communication hole.

The right-hand closing member 42 is formed such that a front cap 42 afor closing the right end opening of the inlet header section body 240and a rear cap 42 b for closing the right end opening of the outletheader section body 250 are integrated with each other via a connectionportion 42 c. The front cap 42 a of the right-hand closing member 42 hasan integrally formed upper leftward-projecting portion 62 to be fittedinto a space of the inlet header section body 240 located above theintra-inlet-header-section flow-dividing control wall 51 b, and anintegrally formed lower leftward-projecting portion 80 to be fitted intoa space of the inlet header section body 240 located below theintra-inlet-header-section flow-dividing control wall 51 b. The upperleftward-projecting portion 62 and the lower leftward-projecting portion80 are vertically spaced apart from each other. Similarly, the rear cap42 b has an integrally formed upper leftward-projecting portion 63 to befitted into a space of the outlet header section body 250 located abovethe intra-outlet-header-section flow-dividing control wall 52 b, and anintegrally formed lower leftward-projecting portion 64 to be fitted intoa space of the outlet header section body 250 located below theintra-outlet-header-section flow-dividing control wall 52 b. The upperleftward-projecting portion 63 and the lower leftward-projecting portion64 are vertically spaced apart from each other. A refrigerant inlet 66is formed in a projecting end wall of the upper leftward-projectingportion 62 of the front cap 42 a of the right-hand closing member 42.Similarly, a refrigerant outlet 67 is formed in a projecting end wall ofthe upper leftward-projecting portion 63 of the rear cap 42 b.Engagement fingers 65 projecting leftward are formed integrally with theright-hand closing member 42 at a connection portion between a frontside edge and a top edge of the right-hand closing member 42, at aconnection portion between the front side edge and a bottom edge, at aconnection portion between a rear side edge and the top edge, and at aconnection portion between the rear side edge and the bottom edge,respectively. The engagement fingers 65 are engaged with the first andsecond members 38 and 39.

As shown in FIGS. 7 to 9, an upwardly projecting first engagement maleportion 1 is formed integrally with the right-hand closing member 42 ata front-rear-direction central portion of the upper end of theconnection portion 42 c. Similarly, a downwardly projecting secondengagement male portion 2 is formed integrally with the right-handclosing member 42 at a front-rear-direction central portion of the lowerend of the connection portion 42 c. In the course of manufacture of theevaporator 20, in a state before assembly of the right-hand closingmember 42 and the joint plate 43, the second engagement male portion 2projects rightward. The rightward-projecting second engagement maleportion is denoted by reference numeral 2A in FIG. 9 (represented by thephantom line). Furthermore, cutouts 3 are formed in the right-handclosing member 42 at front and rear end portions of a bottom edgeportion of the right-hand closing member 42. The right-hand closingmember 42 is brazed to the first and second members 38 and 39 byutilization of its own brazing material layers.

The joint plate 43 has a short, cylindrical refrigerant inflow port 68communicating with the refrigerant inlet 66 of the right-hand closingmember 42, and a short, cylindrical refrigerant outflow port 69communicating with the refrigerant outlet 67 of the right-hand closingmember 42. Each of the refrigerant inflow port 68 and the refrigerantoutflow port 69 includes a circular through-hole and arightward-projecting short, cylindrical portion formed integrally aroundthe circular through-hole.

A slit 4 extending in the vertical direction and adapted to preventshort circuit is formed in a portion of the joint plate 43 between therefrigerant inflow port 68 and the refrigerant outflow port 69. Also,generally trapezoidal through-holes 5 and 6 are formed in the portion ofthe joint plate 43 in such a manner as to be connected to the upper andlower ends, respectively, of the slit 4. Furthermore, a portion of thejoint plate 43 located above the upper through-hole 5 and a portion ofthe joint plate 43 located below the lower through-hole 6 are bent insuch a U-shaped fashion as to project leftward (toward the right-handclosing member 42), thereby forming first and second engagement femaleportions 7 and 8, respectively. The first engagement male portion 1 ofthe right-hand closing member 42 is inserted into the first engagementfemale portion 7 from underneath for engagement, and the secondengagement male portion 2 of the right-hand closing member 42 isinserted into the second engagement female portion 8 from above forengagement, thereby preventing movement of the joint plate 43 in theleft-right direction. The second engagement male portion 2 of theright-hand closing member 42 in a rightward projecting conditionrepresented by the phantom line of FIG. 9 is inserted into the lowerthrough-hole 6 and then bent downward; in other words, the secondengagement male portion 2 is inserted into the second engagement femaleportion 8 from above. The first engagement female portion 7 is engagedwith front and rear portions of the connection portion 42 c of theright-hand closing member 42 which are located on front-rear-directionopposite sides of the first engagement male portion 1, therebypreventing downward movement of the joint plate 43. Furthermore,engagement fingers 9 projecting leftward are formed integrally with thejoint plate 43 at front and rear end portions of a bottom edge of thejoint plate 43. The engagement fingers 9 are engaged with the right-handclosing member 42 while being fitted into the respective cutouts 3formed in the bottom edge of the right-hand closing member 42, therebypreventing movement of the joint plate 43 in the upward direction and inthe front-rear direction. While the joint plate 43 is engaged with theright-hand closing member 42 in such a manner that movement thereof inthe left-right direction, the vertical direction, and the front-reardirection is prevented, the joint plate 43 is brazed to the right-handclosing member 42 by utilization of the brazing material layers of theright-hand closing member 42.

A diameter-reduced portion formed at one end portion of the refrigerantinlet pipe 27 is inserted into and brazed to the refrigerant inflow port68 of the joint plate 43. Similarly, a diameter-reduced portion formedat one end portion of the refrigerant outlet pipe 28 is inserted intoand brazed to the refrigerant outflow port 69 of the joint plate 43.Although unillustrated, an expansion valve attachment member is joinedto the other end portions of the refrigerant inlet and outlet pipes 27and 28 in such a manner as to face the ends of the pipes 27 and 28.

As shown in FIGS. 2, 3, 10, and 11, the refrigerant turn header tank 23is formed from an aluminum brazing sheet having a brazing material layeron each of opposite sides thereof and includes a first member 73 whichhas a plate-like shape and to which all the heat exchange tubes 34 areconnected; a second member 74 formed from a bare aluminum extrudate andcovering the lower side of the first member 73; closing members 75 and76 formed from an aluminum brazing sheet having a brazing material layeron each of opposite sides thereof and brazed to the opposite ends of thefirst and second members 73 and 74; and a communication member 77 formedfrom an aluminum bare material, elongated in the front-rear direction,and brazed to the outer surface of the right-hand closing member 76 insuch a manner as to face the ends of the first intermediate headersection 30 and the second intermediate header section 31. The firstintermediate header section 30 and the second intermediate headersection 31 communicate with each other at their right end portions viathe communication member 77.

The first member 73 includes a first header formation portion 78, whichassumes an upward bulging form and forms an upper portion of the firstintermediate header section 30; a second header formation portion 79,which assumes an upward bulging form and forms an upper portion of thesecond intermediate header section 31; and a connection wall 81, whichconnects a rear end portion of the first header formation portion 78 anda front end portion of the second header formation portion 79 and formsan upper portion of the connection section 32. Inclined walls 78 a and79 a are provided at the front-rear-direction inside of the first andsecond header formation portions 78 and 79 and are inclined in such amanner as to fan out upward and in the front-rear direction. Theinclined walls 78 a and 79 a and the connection wall 81 form a draingutter 33 whose side surfaces are inclined in such a manner as to fanout upward and in the front-rear direction. A plurality of tubeinsertion holes 82 elongated in the front-rear direction are formed inthe first and second header formation portions 78 and 79 atpredetermined intervals in the left-right direction. The tube insertionholes 82 of the first header formation portion 78 and those of thesecond header formation portion 79 are identical in position in theleft-right direction. End portions, located on a side toward theconnection section 32, of the tube insertion holes 82; i.e., rear endportions of the tube insertion holes 82 of the first header formationportion 78 and front end portions of the tube insertion holes 82 of thesecond header formation portion 79, are located in the inclined walls 78a and 79 a, respectively. Thus, the end portions, located on the sidetoward the connection section 32, of the tube insertion holes 82 arelocated in the side surfaces of the drain gutter 33. Drain grooves 83are formed on the first and second header formation portions 78 and 79on the front side of the corresponding tube insertion holes 82 of thefirst header formation portion 78 and on the rear side of thecorresponding tube insertion holes 82 of the second header formationportion 79 in such a manner as to be connected to front end portions ofthe corresponding tube insertion holes 82 of the first header formationportion 78 and in such a manner as to be connected to rear end portionsof the corresponding tube insertion holes 82 of the second headerformation portion 79, as well as in such a manner that the bottom ofeach drain groove 83 extends gradually downward as the distance from thecorresponding tube insertion hole 82 increases. Lower end portions ofthe heat exchange tubes 34 of the front and rear heat exchange tubegroups 35 of the heat exchange core section 21 are inserted into thecorresponding tube insertion holes 82 of the first and second headerformation portions 78 and 79 and brazed to the first member 73 byutilization of the brazing material layers of the first member 73. Thus,the lower end portions of the heat exchange tubes 34 of the front heatexchange tube group 35 are connected to the first intermediate headersection 30 in a communicating condition, whereas the lower end portionsof the heat exchange tubes 34 of the rear heat exchange tube group 35are connected to the second intermediate header section 31 in acommunicating condition. A plurality of drain through-holes 84 elongatedin the left-right direction are formed in the connection wall 81 of thefirst member 73 at intervals in the left-right direction. Also, aplurality of fixation though-holes 85 are formed in the connection wall81 of the first member 73 at intervals in the left-right direction whilebeing shifted from the drain through-holes 84. The first member 73 hasthe same shape as that of the first member 38 of the refrigerantinlet/outlet header tank 22. The first members 73 and 38 are disposed ina mirror image relation.

The second member 74 includes a first header formation portion 86, whichassumes a downward bulging form and forms a lower portion of the firstintermediate header section 30; a second header formation portion 87,which assumes a downward bulging form and forms a lower portion of thesecond intermediate header section 31; and a connection wall 88, whichconnects the first and second header formation portions 86 and 87 and isbrazed to the connection wall 81 of the first member 73 to form theconnection section 32. The second header formation portion 87 has ahorizontal flow-dividing control wall 87 b, which integrally connectsupper end portions of front and rear walls 87 a of the second headerformation portion 87 and vertically divides the interior of the secondintermediate header section 31 into two spaces 31A and 31B. A pluralityof circular refrigerant passage holes 89 in a through-hole form areformed in a rear portion of the flow-dividing control wall 87 b atintervals in the left-right direction. The distance between the adjacentcircular refrigerant passage holes 89 increases gradually as thedistance from the right end of the flow-dividing control wall 87 bincreases. Notably, the distance between the adjacent circularrefrigerant passage holes 89 may be constant. A plurality of drainthrough-holes 91 elongated in the left-right direction are formed in theconnection wall 88 of the second member 74 in alignment with thecorresponding drain through-holes 84 of the first member 73. Also, aplurality of projections 92 projecting upward are formed on theconnection wall 88 in alignment with the corresponding fixationthrough-holes 85 of the first member 73 and are fitted into thecorresponding fixation through-holes 85. The first member 73 and thesecond member 74 are assembled together as follows. The first and secondmembers 73 and 74 are tentatively assembled together such that theprojections 92 are tightly inserted into the corresponding fixationthrough-holes 85. In this tentatively assembled condition, byutilization of the brazing material layers of the first member 73, thefirst and second members 73 and 74 are assembled together such thatfront end portions of the first header formation portions 78 and 86,rear end portions of the second header formation portions 79 and 87, andthe connection walls 81 and 88 are respectively brazed together. Thesecond member 74 has the same shape as that of the second member 39 ofthe refrigerant inlet/outlet header tank 22 except that the refrigerantpassage holes 89 differ in shape and position from the refrigerantpassage holes 54A and 54B and that the counterpart of theintra-inlet-header-section flow-dividing control wall 51 b is absent.The second members 74 and 39 are disposed in a mirror image relation.The second members 74 and 39 are formed from the same extrudate.

The first header formation portion 78 of the first member 73 and thefirst header formation portion 86 of the second member 74 form a hollow,first intermediate header section body 300 whose opposite ends are open.The second header formation portion 79 of the first member 73 and thesecond header formation portion 87 of the second member 74 form ahollow, second intermediate header section body 310 whose opposite endsare open.

The left-hand closing member 75 is formed such that a front cap 75 a forclosing the left end opening of the first intermediate header sectionbody 300 and a rear cap 75 b for closing the left end opening of thesecond intermediate header section body 310 are integrated with eachother. The front cap 75 a has an integrally formed rightward projectingportion 93 to be fitted into the first intermediate header section body300. Similarly, the rear cap 75 b has an integrally formed upperrightward-projecting portion 94 to be fitted into a space of the secondintermediate header section body 310 located above the flow-dividingcontrol wall 87 b, and an integrally formed lower rightward-projectingportion 95 to be fitted into a space of the second intermediate headersection body 310 located below the flow-dividing control wall 87 b. Theupper rightward-projecting portion 94 and the lower rightward-projectingportion 95 are vertically spaced apart from each other. Engagementfingers 100 projecting rightward are formed integrally with theleft-hand closing member 75 at a connection portion between a front sideedge and a top edge of the left-hand closing member 75, at a connectionportion between the front side edge and a bottom edge, at a connectionportion between a rear side edge and the top edge, and at a connectionportion between the rear side edge and the bottom edge, respectively.The engagement fingers 100 are engaged with the first and second members73 and 74. The left-hand closing member 75 is brazed to the first andsecond members 73 and 74 by utilization of its own brazing materiallayers.

The right-hand closing member 76 is formed such that a front cap 76 afor closing the right end opening of the first intermediate headersection body 300 and a rear cap 76 b for closing the right end openingof the second intermediate header section body 310 are integrated witheach other. The front cap 76 a has an integrally formed leftwardprojecting portion 96 to be fitted into the first intermediate headersection body 300. Similarly, the rear cap 76 b has an integrally formedupper leftward-projecting portion 97 to be fitted into a space of thesecond intermediate header section body 310 located above theflow-dividing control wall 87 b, and an integrally formed lowerleftward-projecting portion 98 to be fitted into a space of the secondintermediate header section body 310 located below the flow-dividingcontrol wall 87 b. The upper leftward-projecting portion 97 and thelower leftward-projecting portion 98 are vertically spaced apart fromeach other. Engagement fingers 99 projecting leftward are formedintegrally with the right-hand closing member 76 at a connection portionbetween a front side edge and a top edge of the right-hand closingmember 76, at a connection portion between the front side edge and abottom edge, at a connection portion between a rear side edge and thetop edge, and at a connection portion between the rear side edge and thebottom edge, respectively. Also, engagement fingers 104 projectingrightward are formed integrally with the right-hand closing member 76 atfront and rear end portions of the upper edge of the right-hand closingmember 76. The rightward-projecting engagement fingers 104 are bentdownward so as to be engaged with an upper edge portion of thecommunication member 77. The engagement finger 104 projecting rightwardis formed integrally with the right-hand closing member 76 at afront-rear-direction central portion of the lower end of the right-handclosing member 76. The rightward-projecting engagement finger 104 isbent upward so as to be engaged with a lower edge portion of thecommunication member 77. A refrigerant outflow port 101 through which arefrigerant flows out from the first intermediate header section 30 isformed in a projecting end wall of the leftward projecting portion 96 ofthe front cap 76 a of the right-hand closing member 76. Similarly, arefrigerant inflow port 102 through which the refrigerant flows into thelower space 31B of the second intermediate header section 31 locatedbelow the flow-dividing control wall 87 b is formed in a projecting endwall of the lower leftward-projecting portion 98 of the rear cap 76 b.Also, a guide portion 103 which is inclined or curved upward; in thepresent embodiment, curved upward, toward the interior of the secondintermediate header section 31 is formed integrally with a lower portionof a circumferential portion of the refrigerant inflow port 102 of thelower leftward-projecting portion 98 of the rear cap 76 b. The guideportion 103 guides upward (toward the flow-dividing control wall 87 b)the refrigerant which flows into the lower space 31B of the secondintermediate header section 31 located below the flow-dividing controlwall 87 b. The right-hand closing member 76 is brazed to the first andsecond members 73 and 74 by utilization of its own brazing materiallayers.

The communication member 77 is formed from an aluminum bear material bypress work and assumes, as viewed from the right, a plate-like formidentical with that of the right-hand closing member 76. A peripheraledge portion of the communication member 77 is brazed to the outersurface of the right-hand closing member 76 by utilization of thebrazing material layers of the right-hand closing member 76. An outwardbulging portion 105 is formed on the communication member 77 so as toestablish communication between the refrigerant outflow port 101 and therefrigerant inflow port 102 of the right-hand closing member 76. Theinterior of the outward bulging portion 105 serves as a communicationchannel for establishing communication between the refrigerant outflowport 101 and the refrigerant inflow port 102 of the right-hand closingmember 76. Cutouts 106 are formed in the communication member 77 atfront and rear end portions of the upper edge of the communicationmember 77 and at a front-rear-direction central portion of the loweredge, respectively. The engagement fingers 104 of the right-hand closingmember 76 are fitted into the corresponding cutouts 106.

In manufacture of the evaporator 20, component members thereof excludingthe refrigerant inlet pipe 27 and the refrigerant outlet pipe 28 areprovisionally assembled together, and the resultant assembly issubjected to batch brazing.

The evaporator 20, together with a fixed-capacity-type compressor and acondenser serving as a refrigerant cooler, constitutes a refrigerationcycle which uses a chlorofluorocarbon-based refrigerant. Thisrefrigeration cycle is installed in a vehicle, such as an automobile, asa car air conditioner.

In the evaporator 20 described above, while the fixed-capacity-typecompressor is ON, a two-phase refrigerant of vapor-liquid phase havingpassed through a compressor, a condenser, and an expansion valve entersthe upper space 24A of the refrigerant inlet header section 24 of therefrigerant inlet/outlet header tank 22 from the refrigerant inlet pipe27 through the refrigerant inflow port 68 of the joint plate 43 and therefrigerant inlet 66 of the front cap 42 a of the right-hand closingmember 42. The refrigerant having entered the upper space 24A of therefrigerant inlet header section 24 flows leftward and enters the lowerspace 24B through the communication hole 70 and through theflow-division-adjusting holes 60.

The refrigerant having entered the lower space 24B dividedly flows intothe refrigerant channels 34 a of the heat exchange tubes 34 of the frontheat exchange tube group 35. The refrigerant having flown into therefrigerant channels 34 a of the heat exchange tube 34 flows downwardthrough the refrigerant channels 34 a and enters the first intermediateheader section 30 of the refrigerant turn header tank 23. Therefrigerant having entered the first intermediate header section 30flows rightward and then flows through the refrigerant outflow port 101of the front cap 76 a of the right-hand closing member 76, thecommunication channel in the outward bulging portion 105 of thecommunication member 77, and the refrigerant inflow port 102 of the rearcap 76 b, thereby turning its flow direction and entering the lowerspace 31B of the second intermediate header section 31.

The refrigerant having entered the lower space 31B of the secondintermediate header section 31 flows leftward; enters the upper space31A through the circular refrigerant passage holes 89 of theflow-dividing control wall 87 b; and dividedly flows into therefrigerant channels 34 a of all the rear heat exchange tubes 34. At thetime of entry of the refrigerant into the lower space 31B, while beingguided by the guide portion 103, the refrigerant flows leftward in anobliquely upward direction; i.e., into the interior of the lower space31B while being biased toward the flow-dividing control wall 87 b. Byvirtue of this combined with the feature that the distance between theadjacent circular refrigerant passage holes 89 formed in theflow-dividing control wall 87 b increases as the distance from the rightend of the flow-dividing control wall 87 b increases, the refrigerantwhich flows into the upper space 31A through the refrigerant passageholes 89 is distributed uniformly in the left-right direction as opposedto the case where the guide portion 103 is not provided. Accordingly,the refrigerant flows into the heat exchange tubes 34 connected to thesecond intermediate header section 31 easily in a uniformly dividedcondition; thus, nonuniform distribution of the refrigerant in the heatexchange core section 21 becomes unlikely to arise. Therefore, thetemperature of air having passed through the heat exchange core section21 is homogenized, thereby improving heat exchange performance.

The refrigerant having flown into the refrigerant channels 34 a of theheat exchange tubes 34 flows upward, in opposition to the previous flowdirection, through the refrigerant channels 34 a; enters the lower space25B of the refrigerant outlet header section 25; and then enters theupper space 25A through the oblong refrigerant passage holes 54A and 54Bof the intra-outlet-header-section flow-dividing control wall 52 b.

Next, the refrigerant having entered the upper space 25A of therefrigerant outlet header section 25 flows out into the refrigerantoutlet pipe 28 through the refrigerant outlet 67 of the rear cap 42 b ofthe right-hand closing member 42 and through the refrigerant outflowport 69 of the joint plate 43.

While flowing through the refrigerant channels 34 a of the front heatexchange tubes 34 and through the refrigerant channels 34 a of the rearheat exchange tubes 34, the refrigerant is subjected to heat exchangewith air flowing through the air-passing clearances of the heat exchangecore section 21. Then, the refrigerant flows out from the evaporator 20in a vapor phase.

When the fixed-capacity-type compressor is turned OFF, the liquid-phaserefrigerant remaining within the refrigerant channels 34 a of the heatexchange tubes 34 is effectively retained within the refrigerantchannels 34 a by virtue of the capillary effect. This prevents outflowof the liquid-phase refrigerant from the refrigerant channels 34 a ofthe heat exchange tubes 34 in a short period of time. Additionally, evenafter the compressor is turned OFF, while the liquid-phase refrigerantremains within the refrigerant channels 34 a of the heat exchange tubes34 of the evaporator 20, heat exchange continues between the remainingliquid-phase refrigerant and air passing through the evaporator 20, sothat an abrupt increase in discharge air temperature can be restrained.

FIG. 12 shows, by the solid line, variation of discharge air temperaturewhen the fixed-capacity-type compressor is turned ON and OFF in a carair conditioner which uses the evaporator 20. As is apparent from FIG.12, use of the evaporator 20 shows a gentle increase in discharge airtemperature after the compressor is turned OFF as opposed to variationin discharge air temperature when a fixed-capacity-type compressor isturned ON and OFF in a car air conditioner which uses the evaporatordisclosed in the aforementioned publication, as represented by thebroken line in FIG. 12. Accordingly, in the case where the compressor iscontrolled on the basis of discharge air temperature of the evaporator20, even when the preset high temperature T2 is set lower than thepreset high temperature t2 of the evaporator disclosed in theaforementioned publication, the cycle of turning ON and OFF thecompressor can have the same period as in the case where the compressoris used in combination with the evaporator disclosed in theaforementioned publication. As a result, the temperature differencebetween air discharged into a compartment of an automobile when thecompressor is turned ON and that when the compressor is turned OFF canbe reduced, thereby improving comfort in the compartment. Furthermore,even when the temperature difference between the preset high temperatureT2 and the preset low temperature T1 is reduced by means of lowering thepreset high temperature T2, the cycle of turning ON and OFF thecompressor can have the same period as in the case of the evaporatordisclosed in the aforementioned publication. Therefore, as opposed tothe case where the evaporator disclosed in the aforementionedpublication is used, the compressor does not frequently go ON and OFF,so that the fuel economy of an automobile is not adversely effected.

Next, examples of an evaporator according to the present invention,together with a comparative example, will be described.

EXAMPLE 1

The evaporator 20 was prepared which employed the heat exchange tubes 34each having the configuration shown in FIG. 4; i.e., the number of therefrigerant channels 34 a is 11, and the number of the protrusions 346on the inner peripheral surface of each of the refrigerant channels 34 aexcluding the opposite-end refrigerant channels 34 a is 4.

EXAMPLE 2

An evaporator was prepared which employed heat exchange tubes 34A eachhaving the configuration shown in FIG. 13 a; i.e., the number of therefrigerant channels 34 a is 14, and the number of the protrusions 346on the inner peripheral surface of each of the refrigerant channels 34 aexcluding the opposite-end refrigerant channels 34 a is 4.

EXAMPLE 3

An evaporator was prepared which employed heat exchange tubes 34B eachhaving the configuration shown in FIG. 13 b; i.e., the number of therefrigerant channels 34 a is 16, and the number of the protrusions 346on the inner peripheral surface of each of the refrigerant channels 34 aexcluding the opposite-end refrigerant channels 34 a is 4.

EXAMPLE 4

An evaporator was prepared which employed heat exchange tubes 34C eachhaving the configuration shown in FIG. 13 c; i.e., the number of therefrigerant channels 34 a is 18, and the number of the protrusions 346on the inner peripheral surface of each of the refrigerant channels 34 aexcluding the opposite-end refrigerant channels 34 a is 4.

EXAMPLE 5

An evaporator was prepared which employed heat exchange tubes 34D eachhaving the configuration shown in FIG. 13 d; i.e., the number of therefrigerant channels 34 a is 20, and the number of the protrusions 346on the inner peripheral surface of each of the refrigerant channels 34 aexcluding the opposite-end refrigerant channels 34 a is 4.

COMPARATIVE EXAMPLE

An evaporator was prepared which employed heat exchange tubes 34E eachhaving the configuration shown in FIG. 13 e; i.e., the number of therefrigerant channels 34 a is 7, and the number of the protrusions 346 onthe inner peripheral surface of each of the refrigerant channels 34 aexcluding the opposite-end refrigerant channels 34 a is 4.

The heat exchange tubes 34, 34A, 34B, 34C, 34D, and 34E used in theevaporators of Examples 1 to 5 and Comparative Example have a width W of17 mm as measured in the front-rear direction and a tube height H, whichis a thickness as measured in the left-right direction, of 1.4 mm. Table1 shows the following characteristic values of the heat exchange tubes34, 34A, 34B, 34C, 34D, and 34E: the total cross-sectional area of theplurality of refrigerant channels 34 a; the total cross-sectional,perimetric length of the plurality of refrigerant channels 34 a; theequivalent diameter Dh; and the value A in pieces/mm obtained bydividing the number N of the refrigerant channels 34 a by the width W asmeasured in the front-rear direction (A=N/W).

Evaluation Test:

The evaporators of Examples 1 to 5 and Comparative Example wereincorporated into a refrigeration cycle and were examined for coolingperformance while a fixed-capacity-type compressor was ON. Also, theevaporators were examined for the amount of a liquid-phase refrigerantremaining within the refrigerant channels 34 a of the heat exchangetubes 34, 34A, 34B, 34C, 34D, and 34E. Furthermore, the evaporators wereexamined for time which elapsed after the elapse of 5 seconds after thefixed-capacity-type compressor was turned OFF, until the liquid-phaserefrigerant remaining within the refrigerant channels 34 a of the heatexchange tubes 34, 34A, 34B, 34C, 34D, and 34E evaporated. Table 1 showsthe results of the examinations, and FIGS. 14 and 15 show therelationship of the equivalent diameter Dh with cooling performance andthe amount of remaining liquid-phase refrigerant and the relationship ofthe number of the refrigerant channels 34 a with cooling performance andthe amount of remaining liquid-phase refrigerant, respectively. In FIGS.14 and 15, the solid line indicates cooling performance, and the brokenline indicates the amount of remaining liquid-phase refrigerant. Coolingperformance is represented in percentage based on the coolingperformance of Example 2 which is taken as 100%. The amount ofliquid-phase refrigerant remaining within the refrigerant channels 34 aof the heat exchange tubes 34, 34A, 34B, 34C, 34D, and 34E as measuredafter the elapse of 5 seconds after the fixed-capacity-type compressorwas turned OFF is represented in percentage based on the amount ofExample 1 which is taken as 100%. If cooling performance falls within arange of 95% to 100% as indicated by the arrow Z in FIGS. 14 and 15, theevaporator can be said to have sufficient performance for use in a carair conditioner.

TABLE 1 Total cross- Total sectional, cross- perimetric sectional lengthof area of all Equivalent Amount of Evaporation all channels channelsdiameter Number of Cooling refrigerant time mm mm² Dh channels/width Aperformance Q after 5 sec Sec Example 1 59.12 11.904 0.8054 0.647 99 1004.40 2 66.92 11.184 0.6685 0.824 100 116.34 4.97 3 72.12 10.704 0.59370.941 99 123.37 5.36 4 77.32 10.224 0.5289 1.059 98 134.48 5.75 5 91.559.090 0.3972 1.176 96 151 6.60 Comparative 40.88 13.536 1.3254 2.429 9273.93 3.04 Example

As is apparent from Table 1 and FIGS. 14 and 15, the evaporators ofExamples 1 to 5—whose heat exchange tubes satisfy the relation0.558≦A≦1.235, where A is a value in pieces/mm obtained by dividing thenumber N of refrigerant channels by the front-rear width W (A=N/W), andthe relation 0.35≦Dh≦1.0, where Dh is an equivalent diameter—exhibitscooling performance better than that of the evaporator of ComparativeExample and has sufficient performance for use in a car air conditioner.Also, the evaporators of Examples 1 to 5 is greater than the evaporatorof Comparative Example in the amount of liquid-phase coolant remainingwithin the refrigerant channels of the heat exchange tubes when thecompressor is turned OFF. This, as mentioned previously, can reduce thetemperature difference between air discharged into a compartment of anautomobile when the compressor is turned ON and that when the compressoris turned OFF, thereby improving comfort in the compartment.

FIGS. 16 to 18 show a modified heat exchange tube. In the followingdescription of the modified heat exchange tube, the upper, lower,left-hand, and right-hand sides of FIGS. 16 to 19 will be referred to as“left,” “right,” “front,” and “rear,” respectively.

In FIGS. 16 and 17, a heat exchange tube 130 is oriented such that itswidth direction coincides with the front-rear direction; assumes a flatform; and has a plurality of refrigerant channels 130 a arranged alongits width direction and each having a rectangular cross section. Theheat exchange tube 130 includes mutually opposed flat left and rightwalls 131 and 132 (a pair of flat walls); front and rear side walls 133and 134 which extend between and over front and rear side ends,respectively, of the left and right walls 131 and 132; and a pluralityof partition walls 135 which are provided between the front and rearside walls 133 and 134 and extend longitudinally and between the leftand right walls 131 and 132 for separating adjacent refrigerant channels130 a from each other. Preferably, the refrigerant channel 130 a has arectangular cross section, and a corner portion of the rectangular crosssection has a radius R of 0.1 mm or less.

The front side wall 133 has a dual structure and includes an outerside-wall-forming elongated projection 136 which is integrally formedwith the front side end of the left wall 131 in a rightward raisedcondition and extends along the entire height of the heat exchange tube130; an inner side-wall-forming elongated projection 137 which islocated inside the outer side-wall-forming elongated projection 136 andis integrally formed with the left wall 131 in a rightward raisedcondition; and an inner side-wall-forming elongated projection 138 whichis integrally formed with the front side end of the right wall 132 in aleftward raised condition. The front side wall 133 has flat inner andouter surfaces. The outer side-wall-forming elongated projection 136 isbrazed to the inner side-wall-forming elongated projections 137 and 138and to the right wall 132 while a right end portion thereof is engagedwith a front side edge portion of the right surface of the right wall132. The inner side-wall-forming elongated projections 137 and 138 arebrazed together while butting against each other. The rear side wall 134is integrally formed with the left and right walls 131 and 132. The rearside wall 134 has flat inner and outer surfaces. A projection 138 a isintegrally formed on the tip end face of the inner side-wall-formingelongated projection 138 of the right wall 132 and extends in thelongitudinal direction of the inner side-wall-forming elongatedprojection 138 along the entire length of the inner side-wall-formingelongated projection 138. A groove 137 a is formed on the tip end faceof the inner side-wall-forming elongated projection 137 of the left wall131 and extends in the longitudinal direction of the innerside-wall-forming elongated projection 137 along the entire length ofthe inner side-wall-forming elongated projection 137. The projection 138a is press-fitted into the groove 137 a.

The partition walls 135 are formed such that partition-wall-formingelongated projections 140 and 141, which are integrally formed with theleft wall 131 in a rightward raised condition, andpartition-wall-forming elongated projections 142 and 143, which areintegrally formed with the right wall 132 in a leftward raisedcondition, are brazed together while the partition-wall-forming elongateprojections 140 and 141 butt against the partition-wall-formingelongated projections 143 and 142, respectively. The left wall 131 hasthe partition-wall-forming elongated projections 140 and 141, which areof different projecting heights and are arranged alternately in thefront-rear direction. The right wall 132 has the partition-wall-formingelongated projections 142 and 143, which are of different projectingheights and are arranged alternately in the front-rear direction. Thepartition-wall-forming elongated projections 140 of a high projectingheight of the left wall 131 and the respective partition-wall-formingelongated projections 143 of a low projecting height of the right wall132 are brazed together. The partition-wall-forming elongatedprojections 141 of a low projecting height of the left wall 131 and therespective partition-wall-forming elongated projections 142 of a highprojecting height of the right wall 132 are brazed together.Hereinafter, the partition-wall-forming elongated projections 140 and142 of a high projecting height of the left and right walls 131 and 132are called the first partition-wall-forming elongated projections.Similarly, the partition-wall-forming elongated projections 141 and 143of a low projecting height of the left and right walls 131 and 132 arecalled the second partition-wall-forming elongated projections. A groove144 (145) is formed on the tip end face of the secondpartition-wall-forming elongated projection 141 (143) of the left wall131 (right wall 132) and extends in the longitudinal direction of thesecond partition-wall-forming elongated projection 141 (143) along theentire length of the second partition-wall-forming elongated projection141 (143). A tip end portion of the first partition-wall-formingelongated projection 142 (140) of the right wall 132 (left wall 131) isfitted into the groove 144 (145) of the second partition-wall-formingelongated projection 141 (143) of the left wall 131 (right wall 132).While tip end portions of the first partition-wall-forming elongatedprojections 140 and 142 of the left and right walls 131 and 132 arefitted into the respective grooves 145 and 144, thepartition-wall-forming elongated projections 140 and 143 are brazedtogether, and the partition-wall-forming elongated projections 141 and142 are brazed together.

Also, in the heat exchange tube 130 shown in FIGS. 16 and 17, each ofall the refrigerant channels 130 a excluding two refrigerant channels130 a located at widthwise opposite ends, or each of all the refrigerantchannels 130 a may have two or more elongated protrusions formed on aninner peripheral surface of the refrigerant channel 130 a and extendingin a longitudinal direction of the refrigerant channel 130 a.

The heat exchange tube 130 is manufactured by use of a tube-formingmetal sheet 150 as shown in FIG. 18 a. The tube-forming metal sheet 150is formed, by rolling, from an aluminum brazing sheet having a brazingmaterial layer on each of opposite sides thereof. The tube-forming metalsheet 150 includes a flat left-wall-forming portion 151(flat-wall-forming portion); a flat right-wall-forming portion 152(flat-wall-forming portion); a connection portion 153 connecting theleft-wall-forming portion 151 and the right-wall-forming portion 152 andadapted to form the rear side wall 134; the inner side-wall-formingelongated projections 137 and 138, which are integrally formed with theside ends of the left-wall-forming and right-wall-forming portions 151and 152 opposite the connection portion 153 in a leftward raisedcondition and which are adapted to form an inner portion of the frontside wall 133; an outer side-wall-forming-elongated-projection formingportion 154, which extends outward from the side end of theleft-wall-forming portion 151 opposite the connection portion 153; and aplurality of partition-wall-forming elongated projections 140, 141, 142,and 143, which are integrally formed with the left-wall-forming andright-wall-forming portions 151 and 152 in a leftward raised conditionand which are arranged at predetermined intervals in the width directionof the tube-forming metal sheet 150. The first partition-wall-formingelongated projections 140 of the left-wall-forming portion 151 and thesecond partition-wall-forming elongated projections 143 of theright-wall-forming portion 152 are located symmetrically with respect tothe centerline of the width direction of the connection portion 153.Similarly, the second partition-wall-forming elongated projections 141of the left-wall-forming portion 151 and the firstpartition-wall-forming elongated projections 142 of theright-wall-forming portion 152 are located symmetrically with respect tothe centerline of the width direction of the connection portion 153. Theprojection 138 a is formed on the tip end face of the innerside-wall-forming elongated projection 138 of the right-wall-formingportion 152, and the groove 137 a is formed on the tip end face of theinner side-wall-forming elongated projection 137 of theleft-wall-forming portion 151. The groove 144 (145), into which a tipend portion of the first partition-wall-forming elongated projection 142(140) of the right-wall-forming portion 152 (left-wall-forming portion151) is fitted, is formed on the tip end face of the secondpartition-wall-forming elongated projection 141 (143) of theleft-wall-forming portion 151 (right-wall-forming portion 152).

The inner side-wall-forming elongated projections 137 and 138 and thepartition-wall-forming elongated projections 140, 141, 142, and 143 areintegrally formed, by rolling, on one side of the aluminum brazing sheetwhose opposite sides are clad with respective brazing materials, wherebya brazing material layer (not shown) is formed on the opposite sidesurfaces and tip end faces of the inner side-wall-forming elongatedprojections 137 and 138 and the partition-wall-forming elongatedprojections 140, 141, 142, and 143; on the inner peripheral surfaces ofthe grooves 144 and 145 of the second partition-wall-forming elongatedprojections 141 and 143; and on the left and right surfaces of theleft-wall-forming and right-wall-forming portions 151 and 152 and theouter side-wall-forming-elongated-projection forming portion 154.

The tube-forming metal sheet 150 is gradually folded at opposite sideedges of the connection portion 153 by a roll forming process (see FIG.18 b) until a hairpin form is assumed. The inner side-wall-formingelongated projections 137 and 138 are caused to butt against each other;tip end portions of the first partition-wall-forming elongatedprojections 140 and 142 are fitted into the respective grooves 145 and144 of the second partition-wall-forming elongated projections 143 and141; and the projection 138 a is press-fitted into the groove 137 a.

Next, the outer side-wall-forming-elongated-projection forming portion154 is folded along the outer surfaces of the inner side-wall-formingelongated projections 137 and 138, and a tip end portion thereof isdeformed so as to be engaged with the right-wall-forming portion 152,thereby yielding a folded member 155 (see FIG. 18 c).

Subsequently, the folded member 155 is heated at a predeterminedtemperature so as to braze together tip end portions of the innerside-wall-forming elongated projections 137 and 138; to braze togethertip end portions of the first and second partition-wall-formingelongated projections 140 and 143; to braze together tip end portions ofthe first and second partition-wall-forming elongated projections 142and 141; and to braze the outer side-wall-forming-elongated-projectionforming portion 154 to the inner side-wall-forming elongated projections137 and 138 and to the right-wall-forming portion 152. Thus ismanufactured the heat exchange tube 130.

FIG. 19 shows another modified heat exchange tube.

In FIG. 19, a heat exchange tube 160 is oriented such that its widthdirection coincides with the front-rear direction; assumes a flat form;and has a plurality of refrigerant channels 160 a arranged along itswidth direction. The heat exchange tube 160 includes mutually opposedflat left and right walls 161 and 162; front and rear side walls 163 and164 which extend between and over front and rear side ends,respectively, of the left and right walls 161 and 162; and a pluralityof partition walls 165 which are provided between the front and rearside walls 163 and 164 and extend longitudinally and between the leftand right walls 161 and 162 for separating adjacent refrigerant channels160 a from each other.

The front side wall 163 has a dual structure and includes an outerside-wall-forming elongated projection 166 which is integrally formedwith the front side end of the left wall 161 in a rightward raisedcondition and extends along the entire height of the heat exchange tube160; and an inner side-wall-forming elongated projection 167 which islocated inside the outer side-wall-forming elongated projection 166 andis integrally formed with the front side end of the right wall 162 in aleftward raised condition and extends along the entire height of theheat exchange tube 160. The rear side wall 164 has a dual structure andincludes an outer side-wall-forming elongated projection 168 which isintegrally formed with the rear side end of the right wall 162 in aleftward raised condition and extends along the entire height of theheat exchange tube 160; and an inner side-wall-forming elongatedprojection 169 which is located inside the outer side-wall-formingelongated projection 168 and is integrally formed with the right sideend of the left wall 161 in a rightward raised condition and extendsalong the entire height of the heat exchange tube 160. Each of the frontand rear side walls 163 and 164 has such an arcuate cross section that acentral portion with respect to the left-right direction projectsoutward. The outer side-wall-forming elongated projections 166 and 168of the front and rear side walls 163 and 164 are brazed to the innerside-wall-forming elongated projections 167 and 169.

A corrugated partition-wall-forming portion 170 is integrally formedbetween a tip end portion of the inner side-wall-forming elongatedprojection 167 of the front wall 163 and a tip end portion of the innerside-wall-forming elongated projection 169 of the rear wall 164. Thepartition-wall-forming portion 170 includes wave crest portions 171brazed to the left wall 161, wave trough portions 172 brazed to theright wall 162, and connection portions 173 connecting together the wavecrest portions 171 and the wave trough portions 172 and serving as thepartition walls 165.

Although unillustrated, the heat exchange tube 160 is manufactured asfollows: a tube-forming metal sheet formed from an aluminum brazingsheet having a brazing material layer on each of opposite sides is bentto yield a folded member, and the folded member is subjected to brazingso as to simultaneously braze together the outer side-wall-formingelongated projections 166 and 168 and the inner side-wall-formingelongated projections 167 and 169, respectively, of the front and rearside walls 163 and 164, the wave crest portions 171 of thepartition-wall-forming portion 170 and the left wall 161, and the wavetrough portions 172 of the partition-wall-forming portion 170 and theright wall 162.

In the above-described embodiment, the evaporator according to thepresent invention is applied to a car air conditioner which uses achlorofluorocarbon-based refrigerant. However, the present invention isnot limited thereto. The present invention may be applied to anevaporator of a car air conditioner which is used in a vehicle, forexample, in an automobile and which includes a compressor, a gas coolerserving as a refrigerant cooler, an intermediate heat exchanger, anexpansion valve, and an evaporator and uses a supercritical refrigerantsuch as CO₂.

1. A heat exchange tube assuming a flat form and having a plurality of channels arranged along a width direction of the heat exchange tube, the heat exchange tube satisfying a relation 0.558≦A≦1.235, where A is a value in pieces/mm obtained by dividing the number N of the channels by a tube width W and is expressed by A=N/W.
 2. A heat exchange tube assuming a flat form and having a plurality of channels arranged along a width direction of the heat exchange tube, the heat exchange tube satisfying a relation 0.35≦Dh≦1.0, where Dh is an equivalent diameter in mm.
 3. A heat exchange tube according to claim 1 or 2, wherein each of all the channels excluding two channels located at widthwise opposite ends has an elongated protrusion formed on an inner peripheral surface of the channel and extending in a longitudinal direction of the channel.
 4. A heat exchange tube according to claim 1 or 2, wherein each of all the channels excluding two channels located at widthwise opposite ends has a rectangular cross section, and a corner portion of the rectangular cross section has a radius R of 0.1 mm or less.
 5. A heat exchange tube according to claim 1 or 2, comprising two flat walls in parallel with each other; first and second side walls extending between and over corresponding side ends of the two flat walls; and partition walls provided between the first and second side walls and extending between the two flat walls and in a longitudinal direction of the two flat walls for separating the adjacent channels from each other; wherein the heat exchange tube is formed from a single metal sheet including two flat-wall-forming portions; a connection portion connecting the two flat-wall-forming portions and adapted to form the first side wall; two side-wall-forming elongated projections provided integrally with and in such a manner as to project from corresponding side ends of the flat-wall-forming portions on sides opposite the connection portion, and adapted to form the second side wall; and a plurality of partition-wall-forming elongated projections provided integrally with the flat-wall-forming portions in such a manner as to project in the same direction as the side-wall-forming elongated projections; the heat exchange tube is formed by folding the metal sheet at the connection portion into a hairpin form such that the side-wall-forming elongated projections butt against each other, and brazing the butting side-wall-forming elongated projections together; and the partition-wall-forming elongated projections of at least either flat-wall-forming portion form the partition walls.
 6. An evaporator comprising a plurality of heat exchange tubes each assuming a flat form, the heat exchange tubes being arranged at intervals along a left-right direction with a width direction of the heat exchange tubes coinciding with a front-rear direction, the heat exchange tubes extending in a vertical direction, and each of the heat exchange tubes having a plurality of refrigerant channels arranged along the width direction, the evaporator satisfying a relation 0.558≦A≦1.235, where A is a value in pieces/mm obtained by dividing the number N of the refrigerant channels of the heat exchange tube by a width W of the heat exchange tube as measured in the front-rear direction and is expressed by A=N/W.
 7. An evaporator comprising a plurality of heat exchange tubes each assuming a flat form, the heat exchange tubes being arranged at intervals along a left-right direction with a width direction of the heat exchange tubes coinciding with a front-rear direction, the heat exchange tubes extending in a vertical direction, and each of the heat exchange tubes having a plurality of refrigerant channels arranged along the width direction, the evaporator satisfying a relation 0.35≦Dh≦1.0, where Dh is an equivalent diameter in mm of the heat exchange tube.
 8. An evaporator according to claim 6 or 7, wherein each of all the refrigerant channels of the heat exchange tube excluding two refrigerant channels located at widthwise opposite ends has an elongated protrusion formed on an inner peripheral surface of the refrigerant channel and extending in a longitudinal direction of the refrigerant channel.
 9. An evaporator according to claim 6 or 7, wherein each of all the refrigerant channels of the heat exchange tube excluding two refrigerant channels located at widthwise opposite ends has a rectangular cross section, and a corner portion of the rectangular cross section has a radius R of 0.1 mm or less.
 10. An evaporator according to claim 6 or 7, wherein each of the heat exchange tubes comprises two flat walls in parallel with each other; first and second side walls extending between and over corresponding side ends of the two flat walls; and partition walls provided between the first and second side walls and extending between the two flat walls and in a longitudinal direction of the two flat walls for separating the adjacent refrigerant channels from each other; the heat exchange tube is formed from a single metal sheet including two flat-wall-forming portions; a connection portion connecting the two flat-wall-forming portions and adapted to form the first side wall; two side-wall-forming elongated projections provided integrally with and in such a manner as to project from corresponding side ends of the flat-wall-forming portions on sides opposite the connection portion, and adapted to form the second side wall; and a plurality of partition-wall-forming elongated projections provided integrally with the flat-wall-forming portions in such a manner as to project in the same direction as the side-wall-forming elongated projections; the heat exchange tube is formed by folding the metal sheet at the connection portion into a hairpin form such that the side-wall-forming elongated projections butt against each other, and brazing the butting side-wall-forming elongated projections together; and the partition-wall-forming elongated projections of at least either flat-wall-forming portion form the partition walls.
 11. An evaporator according to claim 6 or 7, further comprising: a refrigerant inlet/outlet header tank having a refrigerant inlet header section and a refrigerant outlet header section arranged in juxtaposition in the front-rear direction; a refrigerant turn header tank disposed below and apart from the refrigerant inlet/outlet header tank and having a first intermediate header section opposed to the refrigerant inlet header section, and a second intermediate header section opposed to the refrigerant outlet header section and communicating with the first intermediate header section; and a heat exchange core section formed between the refrigerant inlet/outlet header tank and the refrigerant turn header tank; wherein the heat exchange core section comprises a heat exchange tube group consisting of a plurality of heat exchange tubes arranged at intervals in a longitudinal direction of the refrigerant inlet/outlet and turn header tanks and connected, at opposite end portions, to the refrigerant inlet/outlet and turn header tanks, and fins each disposed between adjacent heat exchange tubes; two or more heat exchange tube groups are arranged between the refrigerant inlet/outlet and turn header tanks and in juxtaposition in an air flow direction; and the heat exchange tubes of at least one heat exchange tube group are connected between the refrigerant inlet header section and the first intermediate header section, and the heat exchange tubes of at least one heat exchange tube group are connected between the refrigerant outlet header section and the second intermediate header section. 